MERTHYR made it six victories from seven with a bonus-point victory.
The champions took the lead against the run of play when centre Adam Thomas exploited space to send Kyle Evans over for his fourth try of the season, with Matthew Jarvis adding the extras. Callum Hall reduced the deficit with a penalty but a defensive error allowed Merthyr scrum-half Justin James to sneak over the try line.
Visiting captain Craig Locke followed James over after a lineout.
The first half ended with both sides reduced to 14 men after Neath prop Ryan Thomas and Sam Hobbs, of Merthyr, were sin-binned following...